JPH11251056A - Microwave oven - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a microwave oven which can prevent a magnetron from being destroyed by a temperature rise caused by abnormal stoppage of a fan for cooling the magnetron of the microwave oven. SOLUTION: As for a microwave oven which has a magnetron 1, a fan 4 to cool the magnetron 1, a heater 6, a thermistor 7 for temperature detecting to detect a room temperature in a heating compartment 10 heated by the heater 6 and a control means to control them, it is controlled so as to stop heating by detecting abnormal stoppage of the fan 4 while heating by the magnetron 1 by a signal from the thermistor 7 for temperature detecting in order to prevent the magnetron 1 from being damaged.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a structure and a control means for preventing a magnetron cooling fan of a microwave oven from being damaged due to an abnormal stop of the magnetron cooling fan.

[0002]

2. Description of the Related Art A conventional microwave oven has a configuration as shown in FIG. FIGS. 8A and 8B are a side sectional view and a top sectional view of a microwave oven. FIG. 9 is a circuit diagram.

According to these figures, a heater 6 is provided on the ceiling of a heating chamber 10. By heating the heater 6,
The room temperature of the heating chamber 10 rises. A thermistor 7 whose resistance changes with temperature is attached to a part of the ceiling of the heating chamber 10. The signal of the thermistor 7 causes the heating chamber 10
Is controlled.

A magnetron 1 is provided on a side surface of the heating chamber 10, and supplies a high frequency to the heating chamber 10 through the waveguide 3.
When the voltage boosted by the transformer 2 is applied to the magnetron 1, the operation of the magnetron 1 is started. At this time, since the temperature of the magnetron 1 becomes high, cooling is required. Then, the magnetron 1
Has cooled.

[0005] A part of the forcibly blown air is blown into the blow duct 5
, And is blown into the room of the heating room 10. At this time, together with the steam generated due to the heating of the food, the exhaust duct 11
Is released to the outside via The exhaust duct 11 is provided with an absolute humidity sensor 12 and the like as a sensor for detecting the finish, and automates cooking.

Next, an operation state will be described with reference to FIG. When the magnetron 1 operates, it is wired so that the fan 4 always operates. When the magnetron 1 is operating normally by forced air cooling, the anode temperature of the magnetron 1 is about 150 ° C., and the yoke (magnetic yoke) in the outer shell of the magnetron 1 is 70 ° C. or less.

[0007] The fan 4 has a blade attached to a shaded coil type single-phase induction motor. Normal 2500rpm
Rotate about m. However, metal screws, dust, and the like are clogged in the motor (between the rotor and the stator), the motor does not rotate, or the blade attached to the motor is caught and restrained by the wiring, and the fixing screw of the fan 4 is loosened. The rotation of the fan 4 may be stopped, or the rotation speed may be significantly lower than the normal rotation speed.

When the fan 4 stops during the microwave heating operation, no air is sent to the magnetron 1 and the magnetron 1
Rapidly rises in temperature. Several minutes after the fan 4 stops, the anode temperature of the magnetron 1 becomes 300 ° C. or more, and the temperature of the yoke portion becomes 100 ° C. or more. If the anode temperature is higher than this, the maximum rating of the magnetron 1 is exceeded and the life is shortened. If the magnetron 1 is operated without cooling, the magnetron 1 will be destroyed.

At the same time, the temperature of the yoke 1a, which is the outer shell of the magnetron 1, also becomes high, so that the heat-sensitive resin material in the vicinity of the magnetron 1 softens, and in the worst case, it may emit smoke.

[0010] The magnetron 1 is particularly expensive among the components of a microwave oven.
It is inferior in economics. For this reason, there is a need for a safety device in the set.

Conventionally, a thermostat 18 is mounted near the magnetron 1 for the purpose of preventing damage to the magnetron 1 and preventing smoke and the like. In addition to the thermostat 18, there is an abnormal temperature detecting element such as a temperature fuse.

The thermostat 18 is connected in series with the 100 V power supply circuit and the high voltage circuit of the magnetron 1. When the thermostat 18 is turned off, power is not supplied to the magnetron 1 and the operation of the magnetron 1 is stopped. ing.

The thermostat 18 may be directly attached to the yoke 1a of the magnetron. However, as shown in FIG. In short, it is mounted near the magnetron 1 and at a position where the temperature of the magnetron 1 can be transmitted to the thermostat 18 with good responsiveness.

Normally, the sensing temperature of the thermostat and the thermal fuse is appropriately determined in a temperature range of 110 to 145 ° C. in consideration of a margin of variation or the like.

JP-A-2-282621 discloses that a temperature sensor is attached to an exhaust duct to detect overheating of a heating chamber and a magnetron. However, in this case, since the exhaust duct is provided near the magnetron, the flow of the wind in the heating chamber becomes a short circuit path, and the room cannot be sufficiently ventilated. As a result, the door becomes cloudy with steam and visibility becomes poor.

[0016]

However, in the conventional case, an abnormal temperature rise of the magnetron 1 due to the emergency stop of the fan 4 is detected by the thermostat 18, so that the number of parts is large, and the wiring to the thermostat 18 and Assembly processing was required.

When the heater is heated (the magnetron 1 and the fan 4 are not operated) and the room temperature of the heating chamber 10 is set to, for example, 250 to 300 ° C., if the heater heating is continued for a long time, Thermostat 18
Is also high due to heat conduction from the heating chamber 10. When the heater is heated, the thermostat 18 operates,
If the contact of the thermostat 18 is turned off, it is not the original purpose. Therefore, it is necessary to set the sensed temperature of the thermostat 18 so that it does not operate at the time of heating the heater, but operates only when the fan 4 stops at the time of microwave heating.
Although the sensing temperature of the thermostat 18 was set low,
In this case, the responsiveness of the detection when the fan is stopped cannot be increased.

Further, the number of sensing temperatures of the thermostat 18, the thermal fuse, and the like is determined only by the component manufacturer as the component rating. For this reason, it is impossible to freely set the sensing temperature.

The present invention solves the above-mentioned conventional problems. The magnetron 1 is used when the fan is stopped when a thermistor 4 for temperature detection used for heating the heater and a sensor for absolute humidity detection of the thermistor type for automation of cooking are used. It is an object of the present invention to provide a microwave oven used as a sensor for detecting an abnormal rise in temperature.

[0020]

The microwave oven according to the present invention comprises:
In order to solve the above-described problems, the invention according to claim 1 includes a magnetron in a main body, a fan for cooling the magnetron, a heater, and a temperature for detecting an indoor temperature of a heating chamber by the heater. In a thermistor for detection and a microwave oven having control means for controlling these,
The stop of the fan in the heating state by the magtron is detected by a signal from the thermistor for temperature detection,
The heating operation is controlled to be stopped in order to prevent damage to the magnetron.

According to a second aspect of the present invention, the temperature detecting thermistor is housed in a metal pipe, and a part of the metal pipe is inserted into a heating chamber. The mounting plate is fixed to the mounting plate, and the mounting plate is fixed to the yoke of the magnetron.

According to a third aspect of the present invention, the mounting plate is mounted between the outer wall of the heating chamber and a thin material having poor heat conductivity.

According to a fourth aspect of the present invention, in a thermistor-type absolute humidity sensor for detecting water vapor generated from food in a room, punching is provided in a part of a heating chamber close to the magnetron, and the punching is performed through the punching. By disposing the thermistor type absolute humidity sensor on the outer wall of the heating chamber, the stop of the fan in the heating state by the magnetron is detected by a signal from the thermistor type absolute humidity sensor to prevent damage to the magnetron. Therefore, the heating is controlled to be stopped.

According to a fifth aspect of the present invention, the thermistor type absolute humidity sensor is fixed to the mounting plate, and the mounting plate is fixed to a yoke of a magnetron.

[0025]

Embodiments of the present invention will be described below in detail with reference to the drawings.

The microwave oven according to the embodiment of the present invention has a configuration as shown in FIG. 1 (a) and (b)
It is the side sectional view and top view sectional view of a microwave oven. FIG. 2 is a circuit diagram, and FIG. 3 is a sectional view of a main part of a thermistor for temperature adjustment.

According to these figures, a thermistor 7 for temperature adjustment is mounted near the magnetron 1 to operate not only as a temperature control sensor at the time of heating the heater but also to stop rotation of the fan 4 during operation of the magnetron 1. The purpose is to prevent damage due to an abnormal temperature rise of the magnetron 1 when it occurs.

Thermistor 7 for temperature adjustment when heating the heater
Is read by the microcomputer 16 to control the temperature of the heater 6.

As shown in FIG. 3, the thermistor 7 for temperature adjustment is housed in a metal pipe part, pulled out to the outside by a lead wire, and connected to a control circuit. A mounting plate 13 is fixed to a part of the metal pipe by caulking or the like. A part of the metal pipe covering the temperature adjusting thermistor 7 is exposed inside the heating chamber 10,
A room temperature of 0 is detected and the room temperature is controlled. The microcomputer 16 performs control based on a preset temperature so that the relay 22 is turned off when the room temperature is high and turned on when the room temperature is low.

The mounting plate 13 is formed in a U-shape, and a portion facing the thermistor 7 for temperature adjustment is a magnetron 1.
Is attached to the yoke 1a with the screw 14.

The temperature of the yoke 1 a of the magnetron 1 is thermally conducted through the mounting plate 13. Mounting plate 13
It is preferable to use brass, aluminum, or the like having good heat conductivity. The heat transmitted from the yoke 1a of the magnetron 1 to the mounting plate 13 is thermally conducted to the wall surface of the heating chamber 10 (heat is removed), and the heat is not effectively transmitted to the thermistor 7 for temperature adjustment. To reduce the thickness, a thin resin film 15 is put between the thermistor 7 and the wall of the heating chamber 10.
By this resin film 15, the heat of the mounting plate 13 is effectively transmitted to the thermistor 7 for temperature adjustment, and the temperature of the magnetron 1 is detected with high accuracy and responsiveness.

Since a thin film is used, the gap between the heating chamber 10 and the mounting plate 13 is very small.
Does not leak outside.

The operation of the magnetron 1 is as follows.
The process starts when the microcomputer 16 sends a signal to perform N. When the relay 17 is turned on, the fan 4 operates at the same time, and forcibly blows air to the magnetron 1.

FIG. 10 is a flow chart for a means for detecting an abnormal temperature of the thermistor 7 for adjusting the temperature. First, the voltage at the midpoint divided by the thermistor 7 for temperature adjustment and the resistance is sent to the microcomputer 16 and stored as an initial voltage value (V0). After a lapse of a predetermined time (TS), the thermistor voltage V1 is read again.

The voltage difference (V1-V0) of the temperature adjustment thermistor 7 is calculated. The voltage difference (V1-V0)
The value is compared with a numerical value determined in advance as a threshold value (VK). During normal operation in which the fan 4 rotates, the temperature of the magnetron 1 rises little, and (V1-V0) is small. However, when the fan 4 is stopped, the temperature of the magnetron 1 that is not cooled rapidly rises, the temperature of the magnetron 1 is transmitted through the mounting plate 13, and the temperature of the thermistor 7 for temperature adjustment rises. The value of (V1-V0) becomes larger than VK. Then, the microcomputer 16 turns off the relay 17. Heating is stopped and an error message such as a warning display is issued. If (V1−V0) is smaller than VK, the heating is continued as normal. Until the heating time set by the user is reached
This operation is repeated (the values of V1 and V0 are updated of course next time).

Since the thermistor 7 for temperature adjustment is covered with a metal pipe, even if microwaves are supplied to the room by the magnetron 1, it is reflected by the thermistor 7 covered with the metal pipe and is not heated. Because the food is heated,
Since the indoor atmosphere temperature slightly rises, the temperature adjustment thermistor 7 is also slightly warm.

FIG. 11 is a graph showing these characteristics.

Of course, since the magnetron 1 does not operate during the heating of the heater (the relay 17 is turned off), the thermistor 7 for temperature adjustment functions as a temperature detecting element of the heater 6 to control the indoor temperature. The relay 22 is turned ON / OFF in accordance with the set temperature to keep the room temperature constant, and is used for cooking an oven such as a cake or bread.

A microwave oven according to another embodiment has a configuration as shown in FIG. 4A and 4B are a side sectional view and a top sectional view of a microwave oven. FIG.
(A) and (b) illustrate changes in the output VP from the amplifier 19 during normal operation and stop of the fan.
FIG. 6 is a circuit diagram.

According to these figures, the thermistor type absolute humidity sensor 12 is formed by using two thermistors 12a and 12b. Absolute humidity sensors are well known and widely used as finished sensors for automatic cooking of microwave ovens.

FIG. 6 shows a circuit diagram. A bridge circuit is formed by the absolute humidity sensor 12 and the resistor. The midpoint voltage difference of each bridge circuit is amplified by the amplifier 19 and input to the microcomputer 16.

The absolute humidity sensor 17 is attached to the heating chamber 10 near the magnetron 1. The punch 10a is opened on the wall surface of the heating chamber 10, and the absolute humidity sensor 12 is mounted outside the punch 10a. Fixing metal fittings 21 in advance
Are welded to the wall surface of the heating chamber 10.

The food is heated, and steam generated from the food fills the room. The water vapor passing through the punching 10a reaches the absolute humidity sensor 12, and the automatic heating control of the food is performed.

FIG. 5A shows a change in the output VP of the amplifier 19. 9 foods depending on the amount of water vapor from the food
When heated to near 0 ° C., steam is rapidly generated, and VP increases.

However, the voltage A1 across the bridge hardly changes. This voltage A1 indicates the ambient temperature where the absolute humidity sensor 12 is placed. Absolute humidity sensor 1
2 that the temperature can be detected is already
Known at 100.

Next, FIG. 5B shows a graph when the fan 4 stops. At this time, the absolute humidity sensor 12 rapidly transfers heat under the influence of the temperature of the magnetron 1, and the voltage A1 is significantly reduced. However, the output VP of the amplifier 19
Increase is small. Although the food is heated and steam is emitted, since the air is not blown into the heating chamber 10, the circulation of steam is poor and the steam hardly reaches the inside of the punching 10a.

Therefore, by detecting A1 of the absolute humidity sensor 12, an abnormality of the fan 4 is detected.
Of course, the control may be performed based on both the signals A1 and VP.

The present invention is to make effective use of the temperature detection function of the absolute humidity sensor 12 for control, and the detection level is stored in the microcomputer 16 in advance. A free threshold can be selected. In the conventional thermostat 18 and the like, only the sensing temperature specified by a ready-made component manufacturer can be used. Free setting of the threshold value results in accurate detection. In addition, since the component performance of the thermistor 7 is small and the response is good, the stop of the fan 4 can be detected quickly, and damage to the magnetron 1 can be prevented beforehand, and troubles such as smoking can be prevented.

The heater heating is performed at a high temperature such as 200 to 300 ° C. When the yoke 1a of the magnetron 1 is set to stop its operation when the temperature exceeds 100 ° C., the heater heating is performed. Immediately after that, when the microwave heating by the magnetron 1 is performed, the thermistor 7 for temperature adjustment detects high heat, so it is necessary to provide some undetected time before the temperature of the magnetron 1 is detected. Needless to say.

[0050]

As described above, according to the first aspect of the present invention,
According to the described microwave oven, the thermistor normally used for temperature adjustment in the heater heating state is not damaged by the abnormal temperature rise of the magnetron due to the stop of the magnetron cooling fan during microwave heating. It is possible to reduce the number of parts to be used by using the sensor as a detection sensor for preventing noise.

According to the microwave oven of the second aspect of the present invention, since the thermistor is covered with the metal pipe, even if a microwave is supplied into the room, the microwave is reflected and the thermistor itself is hardly heated. , Only the temperature of the magnetron can be detected.

Further, according to the microwave oven of the third aspect of the present invention, since a thin resin material having poor heat conductivity is provided, the temperature from the yoke of the magnetron is transmitted to the thermistor before the temperature is transmitted to the thermistor. There is little heat dissipation and it is transmitted reliably. Also, since the film is thin, the gap between the heating chamber and the mounting plate is very small, and radio waves do not leak outside the heating chamber.

According to the microwave oven according to the fourth aspect of the present invention, an absolute humidity sensor for recognizing a finished state by detecting water vapor generated by heating food is usually used for detecting temperature of a magnetron. It can be shared by using it, and the number of parts can be reduced.

According to the microwave oven of the fifth aspect of the present invention, the temperature from the magnetron can be reliably and instantaneously transmitted, so that the magnetron can be prevented from being damaged.

[Brief description of the drawings]

FIG. 1 is a schematic view of a microwave oven according to an embodiment of the present invention, in which (a) is a side sectional view and (b) is a top sectional view.

FIG. 2 is a circuit diagram of a microwave oven according to an embodiment of the present invention.

FIG. 3 is a sectional view of a main part of a thermistor for adjusting temperature of a microwave oven according to an embodiment of the present invention.

4A and 4B are schematic views of a microwave oven according to another embodiment of the present invention, wherein FIG. 4A is a side sectional view, and FIG. 4B is a top sectional view.

5A and 5B show changes in the output VP of the amplifier of the microwave oven according to another embodiment of the present invention, wherein FIG. 5A shows a normal operation of the fan and FIG.

FIG. 6 is a circuit diagram of a microwave oven according to another embodiment of the present invention.

FIG. 7 is a sectional view of a main part of a thermistor-type humidity detecting sensor of a microwave oven according to another embodiment of the present invention.

8A and 8B are configuration diagrams of a conventional microwave oven, in which FIG. 8A is a side sectional view, and FIG. 8B is a top sectional view.

FIG. 9 is a circuit diagram of a conventional microwave oven.

FIG. 10 is a flowchart of abnormal temperature detection of a thermistor of a microwave oven according to an embodiment of the present invention.

FIG. 11 is a characteristic graph of the microwave oven according to the embodiment of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Magnetron 2 Transformer 3 Waveguide 4 Fan 5 Air blow duct 6 Heater 7 Thermistor 8 Door 9 Control part 10 Heating room 11 Exhaust duct 12 Absolute humidity sensor 13 Mounting plate 14 Screw 15 Film 16 Microcomputer 17 Relay 18 Thermostat 19 Amplifier 20 Mounting plate 21 Fixing bracket 22 Relay

Claims (5)

[Claims] 1. A main body comprising a magnetron, a fan for cooling the magnetron, a heater, a thermistor for detecting a room temperature of a heating chamber by the heater, and control means for controlling these. In the microwave oven, the stop of the fan in the heating state by the magnetron is detected by a signal from the temperature detecting thermistor, and control is performed to stop the heating operation to prevent damage to the magnetron. And microwave oven. 2. The thermistor for temperature detection is housed in a metal pipe, a part of the metal pipe is penetrated into a heating chamber, and the other metal pipe is fixed to a mounting plate. The microwave oven according to claim 1, wherein a plate is fixed to the yoke of the magnetron. 3. The microwave oven according to claim 1, wherein the mounting plate is mounted with a thin material having poor heat conductivity sandwiched between the outer wall of the heating chamber and the mounting plate. 4. A thermistor-type absolute humidity sensor for detecting water vapor generated from food in a room, wherein a punching is provided in a part of a heating chamber close to the magnetron.
By arranging the thermistor type absolute humidity sensor on the outer wall of the heating chamber through the punching, the stop of the fan in the heating state by the magnetron is detected by a signal from the thermistor type absolute humidity sensor, and the magnetron is detected. A microwave oven characterized in that heating is stopped to prevent damage to the microwave oven. 5. The microwave oven according to claim 4, wherein the thermistor type absolute humidity sensor is fixed to the mounting plate, and the mounting plate is fixed to a yoke of the magnetron.